In internal combustion engines, an exhaust gas recirculation is increasingly used to thereby improve the emission values and the efficiency of the internal combustion engine. To avoid here an increase of NOx emissions, it is necessary to cool the recirculated exhaust gases by means of an exhaust gas recirculation cooler, abbr. EGR cooler, since the NOx generation in the combustion process increases disproportionately high with increasing temperature.
Accordingly, an exhaust gas recirculation device, abbr. EGR device, of the type mentioned above comprises typically an EGR cooler which is built into an exhaust gas recirculation line, abbr. EGR line, and which is connected to a cooling circuit operating with liquid coolant. For this, the EGR cooler has a cooler housing, which comprises an exhaust gas inlet, an exhaust gas outlet, a coolant inlet and a coolant outlet, and through which a coolant flows.
From WO 96/30 635 A1 such an EGR device is known, which in addition is characterized in that it has a bypass externally bypassing the EGR cooler and controllable by means of a switching valve. By means of such a bypass, the possibility is provided to bypass the EGR cooler with an activated bypass. This is desired, for example, for a cold start of the internal combustion engine to heat up the internal combustion engine as quickly as possible by means of the heat of the recirculated exhaust gases. With a hot internal combustion engine, the bypass is deactivated so that the recirculated exhaust gases then flow through the EGR cooler, thereby being cooled.
From DE 199 62 863 A1, another EGR device comprising an EGR cooler and a bypass is known. However, in this EGR device, the bypass bypasses the EGR cooler internally. This means that the bypass runs within the cooler housing, but is thermally insulated from the coolant.